Heckelii gets 8-10" so it'd be fine in a 100 gallon tank. Since they're cichlids it's kind of up in the air on how well they do with other fish. Towards conspecifics it seems to be the consensus that they don't do well with each other, usually one killing the other. With other schooling fish, any fish will eat something that can fit in its mouth, but so far with my heck. I haven't seen hi even attempt to nip another fish. I've got mine in with Denison barbs, rainbows, and oto cats and he completely ignores them all.
I'm not sure about sticking them with angels, you could try it but I'd watch it carefully. You would need to have a sand substrate if you went with the heckelii as they do sift through the sand quite a bit.
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